water JULY 2011 43
theme of advocacy versus evidence in the field of public health,
and in particular how this was bedevilling the perception versus
the reality of risk.
Professor Steve Hrudey of the University of Alberta.
Recognising that in developing countries some two million
deaths a year are due to water-related diseases, he noted that
in first-world countries the tremendous success of science and
engineering has virtually eliminated such diseases. Yet there
was still a risk, he stressed, evidenced by some outbreaks in
affluent nations even in the past 10 years, so that the emphasis
must remain on microbiological control.
In the public's mind, the focus is on risks from chemicals,
and the emerging contaminants, he said. Yet a World Health
Organisation (WHO) analysis has identified only five chemicals
that have caused adverse human health outcomes: arsenic,
fluoride, nitrates/nitrites and lead. Advancing chemical analysis
enables values to be placed on the occurrence of many
hundreds of chemicals in water resources, all with names
guaranteed to generate the fear of the unknown in the
general populace. But is there a real risk?
The judgement necessary to interpret risk "opens the door
to a blurring of the boundaries between ... scientific evidence
versus actions driven by public health advocacy ... whether
by scientists or otherwise".
Hrudey particularly addressed the scientists. He granted
that enthusiastic advocacy for a particular hypothesis was
essential to gain financial backing, but cautioned against loss
of objectivity. His experience in scientific publishing does not
generate much confidence, and there is a tendency to 'continue
research until you get the results you want' and dismissal
of negative results as 'random' rather than with the ruthless
scepticism of true science. Nor should correlation be identified
with causation, he continued.
He cited the controversy over chloroform in drinking water.
Following Rook's discovery in 1974 that chlorination produced
trihalomethanes, the National Cancer Institute in 1976 published
evidence that chloroform (in high doses) caused kidney and
liver tumours in rats and mice. Limits were set and many
epidemiogical studies since have assessed the effects on
humans, particularly for bladder cancer. Although the data
are fuzzy, Bull in 2001 concluded that there was no evidence
for lowering of regulated levels. The difference lies in the
recognition of a threshold dose -- ie, a tolerable daily intake
versus a mathematical extrapolation of the effect of high
doses to a zero point.
In 1997 (after research in 1985), the US EPA adopted a
threshold of 300 ug/L -- but many advocacy groups protested
and the EPA backed off. However, on March 31, 2000, the US
District Court ruled that the EPA had violated the Safe Drinking
Water Act by not using the best available science, and the limit
has now been set at 70 ug/L. Yet many water professionals
still believe that any concentration is carcinogenic. One
refereed paper published in 2010 ignored the threshold,
and it is gratifying, but galling for the authors, that they
had to publicly retract it in 2011.
When it comes to media reports the situation is even worse,
he said, and he quoted the furore about birth defects in the
Western Australian press.
The message is clear: do not blindly accept scientists who are
advocating their findings (and yet they must); nor rely completely
on formal refereeing. In conclusion, he recommended a series of
tests to separate evidence from advocacy, based on the advice
promulgated by Carl Sagan in 1995.
The keynote address on the second day was by Patricia
Mulroy, General Manager of the Las Vegas Valley Water District
Southern Nevada Water Authority, which services the desert
city of Las Vegas. With two million residents and approximately
one million visitors per day, Las Vegas relies on the Colorado
River, but has to share its water with six other States and even
with Mexico. The fierce independence of the American settlers
was demonstrated by "First in time, first in (water) right", Mulroy
said, which may have worked for 19th century farmers, but is
impossible for cities.
Patricia Mulroy, General Manager Las Vegas Valley Water District.
Whereas Australia relies to a large extent on markets to share
the Murray-Darling, the seven south-western US states had
to develop the Law of the River. Since this was first drafted in
1922, when Las Vegas was not even dreamed of, negotiations
have been fraught. In 1929, the Hoover Dam backing up Lake
Mead and Lake Powell provided storage and enabled California
to expand to its present dominance, but it was not until 1999
that interstate cooperation replaced strong competition.
For most of this time the two lakes were brimming, with 60
million megalitres of water. However, in 2000 a drought began
and by 2002 the lakes fell first by 15 metres and then by almost
37 metres. This has meant that the two off-takes for Las Vegas
are in jeopardy, and consequently a five-kilometre tunnel under
the river bed is being driven -- a one billion dollar project.
The drought and threat of climate change have finally brought
all the states to the table, and in 2007 a historic agreement
was signed to operate all water resources in full cooperation
for the seven states. Nevada is 'banking' water upstream, and
using Managed Aquifer Recharge (MAR) to seasonally store any
balance of its allocation as treated potable water. There is also
a proposal to develop another groundwater basin, and even a
remote possibility of Nevada operating a desalination plant on
the Mexican coast (rather than in litigious California) to allow
it to make further demands on the river.
-- Special Report